Simulcast radio communication systems are typically employed to provide wide area one-way or two-way radio communication services. In such a system, a source site typically originates (or forwards from another originating site) a signal to be generally broadcast. This signal is routed from the source site to a plurality of remote sites. Each remote site then simultaneously broadcasts the signal in coordination with other remote sites to facilitate reception of the signal by receivers within the area covered by the system.
In this way, a receiver outside the operating range of one remote site may still be within range of one or more other remote sites, thereby reasonably ensuring that the receiver can receive the signal.
One problem with such simulcast systems involves coordinating the various remote sites to ensure that the signals are in fact substantially simultaneously broadcast by each. A failure to achieve this goal will likely result in instances of unacceptable reception coherence, usually caused by carrier frequency differences between the remote sites, deviation control differences, phase differentials with respect to the modulation signal, and the like.
One approach in the past to achieve quasi-synchronous transmission has been to automatically measure and adjust the delay on the distribution path to the individual transmitters. This approach has involved measuring the distribution path delay periodically, and from time to time compensating for the changing delay in each path. It will be appreciated that the delay in each path is due to many sources, including aging and environmental effects. In many cases, particularly dedicated telephone line distribution systems, the distribution path may be changed by telephone company switching equipment, resulting in an immediate and abrupt change in the facility delay. Such a delay change can seriously effect the reception in "non-capture" areas in the system until the change in the facility delay can be detected, measured, and compensated. Moreover, the delay measurement and adjustment procedure itself takes valuable facility time that otherwise would be available for customer traffic. For this reason, it is very desirable to increase the time period between successive facility measurement and adjustments to as long as possible. It would therefore be advantageous to provide an improved method detect a change in the delay of a facility.